string bitmapFileName = openFileDialog1.FileName;

                // Retrieve the bitmap from the file.
                Bitmap bmp = (Bitmap)Image.FromFile(bitmapFileName);

                // Convert the bitmap to an icon.
                Icon ico = Icon.FromHandle(bmp.GetHicon());

                // Generate the icon file name
                string iconFileName = bitmapFileName.Remove(bitmapFileName.Length - 4) + ".ico";

                // Create a file stream to save the icon stream.
                Stream st = new FileStream(iconFileName, FileMode.Create);

                // Create a stream writer to physical write the data to the disk.
                BinaryWriter wr = new BinaryWriter(st);

                // Write the binary icon data to the file stream.
                ico.Save(st);

                // Close the file to write the stream to the disk.
                wr.Close();